Krumm, Robert
Prentice-Hall, 1987
Buku Teks
Stone, M. David
Prentice-Hall, 1984
Buku Teks
Atkins, Robert
Jones and Bartlett , 2009
Buku Teks SO
Prata, Stephen
Sams Publishing , 1987
Buku Teks SO
Tracy, Brian
American Management Association, 2010
eBooks